The excellent websites The Blackboard Where Climate Talk Gets Hot!” and Climate Audit have been discussing in depth the latest anomalies in the in-situ measured surface and satellite measured tropospheric temperatures. This Climate Science weblog is intended to add to this discussion by presenting several issues with respect to these data sets:
1. The quantification of the correlation between the surface and tropospheric temperatures has been examined in several papers including:
Chase, T.N., R.A. Pielke Sr., J.A. Knaff, T.G.F. Kittel, and J.L. Eastman, 2000: A comparison of regional trends in 1979-1997 depth-averaged tropospheric temperatures. Int. J. Climatology, 20, 503-518 [see Section 8]
and, more recently, in
Pielke Sr., R.A., C. Davey, D. Niyogi, S. Fall, J. Steinweg-Woods, K. Hubbard, X. Lin, M. Cai, Y.-K. Lim, H. Li, J. Nielsen-Gammon, K. Gallo, R. Hale, R. Mahmood, S. Foster, R.T. McNider, and P. Blanken, 2007: Unresolved issues with the assessment of multi-decadal global land surface temperature trends. J. Geophys. Res., 112, D24S08, doi:10.1029/2006JD008229 [see Figure 25].
As documented in these papers, the specific values of the anomalies vary between the data sets. Thus while both tend to warm and cool at the same times, the quantitative magnitude of the warming and cooling (and thus the anomalies) differs significantly between the surface and the troposphere.
2. The surface in-situ data that are used to construct the GISS, HadCrut, and NCDC analyses are drawn from essentially the same raw data. They are not indepedent analysis. The main reason that they are different at all is that they use different interpolation and other analysis methods. As we reported in Pielke et al 2007 in Section 7
“The raw surface temperature data from which all of the different global surface temperature trend analyses are derived are essentially the same. The best estimate that has been reported is that 90–95% of the raw data in each of the analyses is the same (P. Jones, personal communication, 2003).”
3. While the focus is on temperature anomalies, it must be recognized that the global average surface and tropospheric temperatures always cool in the Northern Hemisphere Fall. This is shown at the University of Alabama at Huntsville website. For the average day by day change in average temperature for their lower tropospheric analysis from Julian Day 244 (September 1) to Julian Day 273 (September 30) the average global cooling is 0.575C.
Thus the change in an anomaly value between months must be placed within the context of its percent change over this time period relative to the average expected change. For September, for example, a change of an anomaly from August to September of 0.1C is a 17% variance from the average expected change. A positive value (such as reported for this past September) means the global cooling was less than the average cooling rate for this month.
Climate Science looks forward to continued excellent analysis by The Blackboard Where Climate Talk Gets Hot!” and Climate Audit!